EP 0 092 605 B2, for example, describes a rod sensor that has a passive sensor for passively measuring rotational speed by means of induction in brake systems of utility vehicles. During mounting, the rod of this known rod sensor is pushed into the securing opening or through the securing opening until it makes contact with the pole wheel, and is secured in the securing opening by means of a clamping hushing. The measurement principle of the rod sensor by means of induction permits the sensor carrier to be attached in the securing opening in a positionally independent fashion in relation to rotations of the sensor carrier about the rod axis of the rod. This known rod sensor can therefore be installed without complex adjustment operations and therefore at low cost. However, it is disadvantageous that an alternating voltage, which can be measured and evaluated, is induced in the passive sensor only when the pole wheel rotates relative to the rod sensor. The amplitude of the alternating voltage is, moreover, dependent on the rotational speed of the pole wheel, with the result that low rotational speeds, which give rise to an amplitude that is insufficient for measuring the rotational speed, cannot be sensed.
A known sensor device of a different type is used in brake systems in comparatively small or lightweight vehicles, in particular passenger cars, and has an active sensor. Because of the active sensor, this sensor device can supply measured values even when the pole wheel is rotating very slowly or is stationary. However, this sensor device supplies measured values or sufficiently good and reliable measured values only when the active sensor is arranged in a very precisely defined position relative to the pole wheel during mounting. The sensor device or a sensor carrier with the active sensor is therefore fastened, for example, by means of a screw flange, and aligned precisely with respect to the pole wheel. The mounting of the sensor device therefore requires costly adjustment operations and is laborious and expensive.